Atrial fibrillation (AF) is the most common sustained arrhythmia in the world, which currently affects millions of people. In the United States, AF is projected to affect 10 million people by the year 2050. AF is associated with increased mortality, morbidity, and an impaired quality of life, and is an independent risk factor for stroke. The substantial lifetime risk of developing AF underscores the public heath burden of the disease, which in the U.S. alone amounts to an annual treatment cost exceeding $7 billion.
Most episodes in patients with AF are known to be triggered by focal electrical activity originating from within muscle sleeves that extend into the Pulmonary Veins (PV). Atrial fibrillation may also be triggered by focal activity within the superior vena cava or other atrial structures, i.e. other cardiac tissue within the heart's conduction system. These focal triggers can also cause atrial tachycardia that is driven by reentrant electrical activity (or rotors), which may then fragment into a multitude of electrical wavelets that are characteristic of atrial fibrillation. Furthermore, prolonged AF can cause functional alterations in cardiac cell membranes and these changes further perpetuate atrial fibrillation.
Radiofrequency ablation (RFA), laser ablation and cryo ablation are the most common technologies of catheter-based mapping and ablation systems used by physicians to treat atrial fibrillation. Physicians use a catheter to direct energy to either destroy focal triggers or to form electrical isolation lines isolating the triggers from the heart's remaining conduction system. The latter technique is commonly used in what is called pulmonary vein isolation (PVI). However, the success rate of the AF ablation procedure has remained relatively stagnant with estimates of recurrence to be as high as 30% to 50% one-year post procedure. The most common reason for recurrence after catheter ablation is one or more gaps in the PVI lines. The gaps are usually the result of ineffective or incomplete lesions that may temporarily block electrical signals during the procedure but heal over time and facilitate the recurrence of atrial fibrillation.
PV isolation (PVI) can be accomplished in most patients using irrigated ablation catheters, however recurrence of AF may occur over time. Recurrences are thought to be due to PV reconnections from sites that either recovered, gaps in the ablation lines, or ablated sites that did not achieve transmurality during the initial procedure. Therefore, lesion assessment is very important in catheter ablation procedures so that the operator can deliver the best possible lesions during pulmonary vein isolation procedures. The improved quality of the lesions can reduce atrial fibrillation recurrences.
Real-time optical tissue characterization can provide excellent and previously impossible assessment of electrode-tissue contact and lesion progression during ablation. It can also provide highly valuable information regarding the myocardium, collagen, elastin tissue composition at the site of catheter tip and represents a new frontier in the understanding of the complex nature of the biophysics of cardiac ablation. Lesion depth directly correlates to a decrease in fNADH signal intensity. This information should be used to optimize the selection of ablation power and ablation energy application time to maximize lesion formation and improve the success of ablation procedures. Therefore, there is a need for systems and methods for real-time optical tissue characterization.